Study On Metabolites Mediated Plant Resistance Against Diseases And Drought During Interaction Between Bacillus Cereus AR156 And Tomato

Bacillus cereus AR156,known as one plant growth-promoting rhizobacteria strain(PGPR),which is capable to colonize on plant roots and induce systemic resistance(ISR).Previous studies revealed that B.cereus AR156 induces resistance to biotic stress such as Botrytis cinerea and Ralstonia solanacearum in tomato,as well as abiotic stress such as drought.Metabolites play important roles in the interaction between Bacillus cereus AR156 and plants,by helping plants resist diseases and adapt to stresses.Which metabolite of B.cereus AR156 can induce systemic resistance to tomato gray mold caused by Botrytis cinerea?Which metabolite can be recognized by plants and induce the tomato systemic drought tolerance in B.cereus AR156 fermentation broth?What’s the role plant root exudates played in biocontrol against tomato bacterial wilt caused by Ralstonia solanacearum,during the interaction between B.cereus AR156 and tomato plant?In this study,B.cereus AR156 was considered as the BCA(Biocontrol agent)strain,tomato was considered as t model plant;B.cinerea BC1301 and R.solanacearum HN4 were considered as pathogens for investigating the mechanism of metabolites in the interaction between bacillus and tomato.Previous research found that B.cereus AR156 could induce systemic resistance in tomato,and could secrete various secondary metabolites and involved in plant-microbe interaction,such as oxalic acid was the common organic acid that can activate plant’s own defense response at low concentration and prevent Botrytis cinerea.Moreover,B.cereus AR156 could secrete amine metabolites and could be perceived by plant and induce tomato drought tolerance.Other whiles,B.cereus AR156 colonized on tomato plant root and could induce changes of tomato root exudates,and certain specific components such as lactic acid and hexanoic acid will further participate in the biological control process to prevent soil-borne diseases such as tomato bacterial wilt.These results revealed the important role that secondary metabolites played in the interaction between plants and microorganisms.It will be more advantageous to develop high-efficiency biopesticide preparations and promote the rapid development of microbial pesticides if the mechanism of metabolites is clearly.1.Mechanism of organic acid secreted by Bacillus cereus AR156 induces tomato systemic resistance to Botrytis cinereaBacillus cereus AR156 secretes oxalic acid and the oxalic acid is capable to induce systemic resistance to B.cinerea BC1301 in tomato.Besides,defense-related genes Pin2,LOXD and AOS2 and hydrogen peroxide accumulation,callose deposition,and defenseassociated enzyme(SOD,POD,CAT)were induced upon challenge inoculation in leaves primed by oxalic acid.Moreover,genetic epistasis analysis showed that oxalic acid can induce higher resistant to B.cinerea BC1301 in tomato wild type and NahG transgenic tomato plants(unable to accumulate salicylic acid),but not in def-1 mutant plants(reduced ability to accumulate jasmonic acid).Moreover,in oxalic acid-primed tomato,pathogen infection triggered expression of JA,but not the SA signaling defense-related genes.These results indicate that oxalic acid-induced systemic resistance to gray mold is dependent on JA signaling pathway transduction.Thus,we deduced that the oxalic acid secreted by B.cereus AR156 plays an important role in inducing systemic resistance to Botrytis cinerea at low concentrations.2.Study on the mechanism of inducing drought tolerance in tomato by amine compounds secreted by Bacillus cereus AR156Bacillus cereus AR156 can colonize tomato roots and induces drought tolerance in tomato.This part of study found that three amine metabolites(ethanolamine,putrescine and spermidine)were identified by HPLC in AR156 fermentation broth.We tested simulated induced drought resistance in vitro,orthogonal greenhouse experiments and physiological indexes under drought stress,and developed basic formulation(XF01),and then determined the antioxidant enzyme activities and expression of stress-related genes.Results showed three combinations could induce drought tolerance,and the relative water content of leaves,chlorophyll content and recovery intension of roots were significantly improved compared with the control,but the MDA content and relative leaf conductivity were decreased.The drought resistance of these three combinations was above 34%.In addition,the activities of SOD,POD and CAT were increased remarkably after treated with XF01,the expression of MDHAR,APX and rbcS genes remained high in the late drought stage,but P5CS was only higher than that in control group after 5 day and 7 day drought stress then return to normal levels.Besides the tomato survival rate 24 h after re-watering was 79.17%,which was 3.17 times higher than the control group.These results showed that the amines metabolized by B.cereus AR156 could improve the adaptability and resilience of tomato plants to drought stress.3.Plant root exudates are involved in Bacillus cereus AR156 mediated biocontrol against Ralstonia solanacearumBacillus cereus AR156 can induce plant immunity after colonization on plant roots,and effectively control tomato bacterial wilt.This study found that the interaction between AR156 and tomato plants can facilitate composition changes of plant root exudates and these changes directly affect the growth of both plant pathogens HN4 and B.cereus AR156 itself and the biological control ability.In addition,some upregulated metabolites(fructose,lactic acid,D-pinitol,sucrose,threonine,hexanoic acid)in tomato root exudates induced by B.cereus AR156,such as lactic acid and hexanoic acid,induced the growth and motile ability of in vitro B.cereus AR156 cells,and affected the growth and motility of R.solanacearum.Exogenously applying hexanoic acid and lactic acid to tomato plants showed positive biocontrol efficacy(46.6%and 39.36%)against tomato bacterial wilt,compared with 51.02%by B.cereus AR156 itself.Furthermore,fructose,lactic acid,sucrose and threonine at specific concentrations stimulated the biofilm formation of B.cereus AR156 in Luria-BertanGlycerol-Magnesium medium(LBGM),and the colonization of B.cereus AR156 on the tomato root surface in Murashige-Skoog medium(MS).These observations suggest that the ability of B.cereus AR156 to induce some specific components in plant root exudates was probably involved in further biocontrol processes.